[clang] Revise the modules document for clarity (PR #90237)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

I think I've addressed all of the feedback (thank you all for the improvements!), except for the suggestion from @Endilll to switch to using italics rather than code font. I think the suggestion is a good one, but it's a time-consuming edit that doesn't change the meaning of the document, so I'd prefer that be done in a follow-up.

https://github.com/llvm/llvm-project/pull/90237